Vinylphosphonic acid is presently manufactured by a variety of processes which are disadvantageous because they are tedious, cumbersome and/or time-consuming. Furthermore, appropriate raw materials for the production of such compounds are not readily commercially available. As a result, multi-step processes have been employed for the manufacture of vinylphosphonic acid. Such processes generally involve prolonged process times, reduced yields and as a result require additional process steps to purify the desired product.
In particular, vinylphosphonic acid may be prepared by the hydrolysis of dialkyl vinylphosphonates such as dimethyl vinylphosphonate. However, such processes are difficult to practice because dialkyl vinylphosphonates such as dimethyl vinylphosphonate are not readily commercially available.
German Patent No. 2,127,821; U.S. Pat. Nos. 4,388,252 and 4,493,803 as well as related patents describe processes for the manufacture of vinylphosphonic acid by a multi-step process including a thermal elimination reaction. The final product requires purification by solvent extraction such as described in U.S. Pat. No. 5,391,815. The multi-step process is both cumbersome and tedious and illustrates the difficulty in introducing vinyl groups to a phosphorous containing compound.
Another process for producing vinylphosphonic acid is described in PCT/GB2002/003573. This process involves the steam hydrolysis of bis(2-chloroethyl)vinylphosphonate under pressure in the presence of formaldehyde. The process takes a significant period of time to go to completion. The reaction produces a very dark colored product which must be treated by an extensive decolorization procedure to obtain a desired product. The reference process illustrates the difficulty in removing chloroethyl groups from bis(2-chloroethyl)vinylphosphonates.
A. J. Gutierrez et al., Nucleosides, Nucleotides and Nucleic Acids, Vol. 20 page 1299 (2001) describes the dealkylation of phosphonate esters using organosilyl halides as a potential method for the production of phosphonic acids. R. Rabinowitz, J. Org. Chem., Vol. 28, pg. 2975 (1963) describes the conversion of bis(2-chloroethyl)vinylphosphonate to vinylphosphonic acid by reaction with trimethylsilyl chloride. The reaction requires 30 days for completion making it essentially impractical for any meaningful industrial use. This procedure also demonstrates the difficulty in removing chloroethyl groups from this (2-chloroethyl)vinylphosphonate.
H. Gross et al., Journal f. prakt. Chemie, Vol. 320, pg. 344 (1978), C. E. McKenna et al., Tetrahedron Letters, Vol. 2, pg. 155 (1977) and G. M. Blackburn et al., J. C. S. Chem. Comm., pg. 870 (1978) describe the preparation of vinylphosphonic acids from vinylphosphonates by reaction with trimethylsilyl bromide or iodide. However, trimethylsilyl bromide and iodide are expensive laboratory reagents and are not readily commercially available raw materials for mass production of vinylphosphonic acids.
It is noted that the H. Gross et al. reference uses vinylphosphonates and trimethylsilyl bromide in a 1:5 molar ratio rendering even the laboratory process, let alone a commercial process extremely expensive.
Y. Machida et al., Synthetic Communications, Vol. 9, pg. 97 (1979) describes a reaction between vinylphosphonates, triethylsilyl chloride and lithium iodide in a 1:2.4:2.4 molar ratio in carbon tetrachloride as a solvent. The Machida et al. process employs large amounts of lithium iodide and therefore is disadvantageous because of the possibility of excessive metal contamination of the vinylphosphonic acids with lithium.
It would therefore be a significant advance in the art of producing vinylphosphonic acids if a process could be developed which can be readily implemented on a commercial scale without the disadvantages described above characteristic of prior art processes. It would be a further advance in the art to produce silyl ester intermediate products of the desired vinylphosphonic acids.